1. Field of the Invention
The present invention relates to an optical disk player.
2. Description of Background Information
For the optical disk player used for playing disk type recording medium (hereinafter simply referred as "disk") such as a video disk, a digital audio disk, etc., a tracking servo unit for controlling the recording track is indispensable to ensure accurate tracking by the information reading optical spot on the pickup unit irrespectively of the eccentricity of the disk.
Such a tracking servo unit is designed as a closed servo control system, and it generates a tracking error signal corresponding to the deviation of the information reading optical spot in the radial direction of the disk relative to the recording track of the disk, and it further drives the tracking actuator according to the tracking error signal for deviating the information reading optical spot in the radial direction of the disk. Thus, it performs the position control of the information reading optical spot relative to the recording track.
When the optical spot for reading information jumps the recording track in such a servo unit, the servo loop is kept in opened state and an acceleration signal having the polarity corresponding to the jumping direction is supplied to the tracking actuator. The deceleration signal with an opposite polarity to the acceleration signal is supplied to the actuator for a fixed period of time at the zero-cross timing of tracking error signal level during the jumping so that a certain braking power is provided. Then, the servo loop is closed to lead-in the servo loop (Japanese Patent Application Laid Open No. 2-79228).
As the methods for generating tracking error signal, the three-beam method, push-pull method, time difference detection method, etc. are known. Of these methods, the time difference detection method uses the so-called quadrant type photodetector comprising four photoelectric conversion elements, each of which has photodetecting surface divided into 4 parts, as light receiving means for receiving the reflected light beam from the disk, as it is known from the description in the Japanese Provisional Patent Application Laid Open No. 57-181433. Of the phase difference generated between the outputs of these photoelectric conversion elements, the phase variation component, changing according to the deviation of optical spot for reading information in the radial direction of the disk relative to the recording track, is detected, and this phase variation is issued as the tracking error signal. This method is advantageous in that it is not adversely affected by the deviation of the intensity distribution of the reflected light beam from the disk. On the other hand, in the so-called off-track area between the recording tracks, leakage of RF components of the information reading optical spot of the adjacent track occurs because RF components are used for detection, and correct error signal cannot be obtained. Thus, it is disadvantageous in that the zero-cross timing of the tracking error signal level on off-track becomes unstable.